In many circumstances undesirable tissue is removed from internal structures of a patient, for example pre-cancerous or cancerous tissue. Many techniques exist for the removal of undesirable tissue, one example of which is photodynamic therapy (PDT). PDT is a “drug and light” therapy that involves the combined effect of a photosensitizer agent, such as porfimer sodium (Photofrin®), and delivery of laser light to result in ablation of the target tissue.
One challenge in the application of PDT is to predict the effect that PDT will have on a particular patient. While standard doses of drug and light are typically used, the clinical outcomes are quite variable. Some patients have a very aggressive response to treatment. In such cases, PDT applied according to standard recommendations may result in the unintended destruction of healthy tissue. For example, damage to normal tissue from a patient's esophagus can cause severe stricturing of the esophageal lumen that may take numerous endoscopic dilation procedures (or even stent placement) to restore so that the patient can eat and drink and take their medicines by mouth. On the other hand, some patients have a very poor response to treatment when administered the same drug and light dose, and some or all of the target tissue remains despite the time, money and resources spent undergoing PDT.